Download the free DIY tool Dynamic Range Meter 1.1.1) using links under "Software:" on upper right. I use the version for Foobar2000. When you install it, it's fun to go thru your music and see how well it does (and how your hearing/perception) (dis)agrees with its results. You can keep logs, and even submit them to DRD to help further build the database.

Now, DR -- per the mathematical design of THIS tool -- isn't everything as many hard-core anti-loudness folks want to believe. Certainly, many of the early (pre-loudness-era) CDs, so cherished by these folks, have that early-CD hardness/glare that's difficult to ignore. That said, the DRD and its DIY tool is quite useful and practical for a music attribute so fundamental.

Stereophile, several years back ("What's Going on Up There?", Oct. 2000), reported that certain high-rez releases (DVD-A and 24/96 DVDs, I think) were not spectrally extended, as high-rez allows.

Not sure about freq. spectrum, but the DRD reports several titles where HDTracks releases are dynamically "compressed" compared to other mostly older releases, or LP rips, of the same album, of course.

The DR Meter tool, noted above, is quick/easy to use ... and including DR in the product description by HD Tracks or other downloads-seller, helps keep the mastering engineers "in check".